For many years, the Public Switched Telephone Network (PSTN) has provided a reliable mechanism for transmitting voice communications. However, the reliability of conventional telephone networks comes at high cost. Each established communication link in a conventional telephone network, reserves a bandwidth of 64 kbps for the duration, regardless of the bandwidth actually needed for the communications. A conventional telephone communication link uses a bandwidth of 64 kbps for all transmissions.
In contrast, conventional data communication networks are packet-based with no guarantee of reliability. In such a network, bandwidth is available on a first-come, first-serve basis. In a conventional packet-based network, voice communications may be broken into multiple packets. Packets are transmitted and then reassembled at the destination. Because packets may be lost or may arrive out of sequence, the quality of voice communications may suffer.
In the last few years, efforts have been made to converge data, voice, and video communications in a single network. For example, the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) released the H.323 specification for transmitting audio, video, and data across an Internet Protocol (IP) network.